I agree. Game devs are better off targeting proton as a platform, but Linux purists complain if there is no native port and you don't get the brownie points for putting in the effort.
I think there's plenty of brownie points to be had for making sure a game runs well under Proton... There's very little reason that GoG cannot do what Steam does with Proton for Windows games.
That's not the same as a native client that launches games under Proton... GoG would be better served with something native/adaptive (even web/electrion/tauri based) that also installs/manages a Proton install along with the games.